Fractionation in presence of radiant energy



Dec. 7, 1948. c. H. scHLl-:SMAN 2,455,812

FRACTIONATION IN PRESENCE 0F RADIANT ENERGY Filed June 30, 1945 2Sheets-Sheet 1 AEFlI/X v HEAD Dec- 7 1948- c. H. scHLEsMAN 2,455,812

FRCTIONTION IN PRESENCE 0F RADIANT ENERGY Filed June 30, 1945 2Sheets-Sheet 2 y g PROPOI? TIO/VER ATTORNEY Patented Dec. 7, 1948 TENERG Carleton H. Schlesman, Camden, N. J., asslgnor to Socony-VacuumOil Company, Incorporated, a corporation o! New York Application Juneso, 1945, seran No. 302,603

(ci. 19e-94) '5 claims. l This invention relates generally tolfractional distillation and more particularly to a method and apparatusfor the separation of two compounds having almost identical bollingpoints or I compounds which'form constant boilingfmixtures.

This is accomplished by taking advantage oi the well known principlethat chemical compounds having the same vapor pressure differ in theirabsorption of radiant energy and utilizing radiant energy to maintainone of the compounds of a. mixture in its original state whileseparating the other compound therefrom by changing its state, such as,for example, maintaining one compound in liquid state while convertingthe other from a liquid state to a vapor state; maintaining one compoundin a vapor State while converting the other from a vapor state to aliquid state; or maintaining one compound in a liquid state whileconverting the other compound from a liquid state to a frozen solidstate.

In the purication of hydrocarbons and chemical compounds eflicientiractionating columns having as 'many as one hundred theoretical plates,have been found to be important devices for the separation of impuritiesor the separation of one compound from another. The use of suchfractionating columns is not practical in certain cases, such as, forexample, where two compounds having almost identical boiling .points orin the case of compounds which form constant boiling mixtures. Thepresent invention deals with adevice which retains much of thesimplicity and high capacity of the fractionating columns and whichprovides fractionation or separation over and above that possible bydistillation alone.

Prior to this invention a mixture of compounds having almost identicalboiling points orcompounds which form constant boiling mixtures haveposed a problem in the prior art that has been met with a degree ofsuccess by employing azeotropic distillation, solvent extraction., orchemical processes.

The azeotropic distillation process requires at least three additionalsteps in the fractionation if it is desired to separately recover bothcompounds and the azeotrope forming agent, namely.

. the separation of one compound as a fraction from the azeotrope formedby the fraction representing the other compound and the azeotropeforming agent; the separation of the second compound from the constantboiling azeotrope by the addition of a separating agent; and thenseparating the azeotrope forming agent from the last mentionedseparating agent. Since none of thesesteps can be carried out in theregular fractionating column the process necessarily involves the use ofadditional expensive equipment.

The solvent extraction process requires at least two additional stepsthat must be carried out outside the regular fractionation column,namely, introducing a solvent into the mixture which combines with onecompound to separate the mixture into a fraction and a fraction plus thesolvent; and then separating the solvent from the second fraction.

Chemical processes such as those carried out by introducing sulfuricacid into the mixture of two compounds having nearly the same boilingpoints are carried out outside the regular fractionation column andusually result in the loss of one of the compounds.

Obviously any one of the above processes involve considerable additionalequipment and are very expensive.

The present invention, in comparison with the above outlined processesof the prior art. is vthe utmost in simplicity and provides a method ofseparating fractions comprising two compounds of nearly the same boilingpoints or constant boiling mixtures that can be, if desired, carried outright in the top of the regular fractionation column during normalfractional distillation procedure without the necessity of addingazeotrope forming agents, solvent extraction agents or chemical reactionagents, or of later recovering such added reagents.

It is known that chemical compounds having the same vapor pressure dlierin their absorption of radiant energy. conjugate double bonds causeabsorption in the ultra-violet portion of the spectrum. Polar moleculessuch as nitro benzene, CaHsNOz, absorb the radio frequencies. This factis employed to eiect separation. If two compounds produced at theirboiling point are passed over a cooled surface and at the same timeexposed to a high frequency field the compound showing absorption atthat frequency will remain a vapor while the other showing no absorptionwill be condensed. As* an example methyl ethyl ketone CHCOCxHs andisopropyl aannam 3 f alcohol .both having a boiling point of 81 C. canbe separated by the present invention. Since the ketone shows a verystrong absorption or radio frequency radiation, it can be separated as avapor from the alcohol which is recovered as a liquid.

Additionally, 2,2,3-trimethyl butane (triptane) and 2,2-dimetnvl pentaneshow similar boiling points, hence they are very diillcult to separateby distillation. Since triptane shows a strong infrared radiationabsorption in the region oi.' 120,000 angstrom units at which point2,2-dimethyl pentane does not absorb, infra-red radiation absorption ofthis frequency may be employed to eilect separation.

Therefore, the primary object of this invention resides in the provisionof a novel method and apparatus tor separating compounds having the sameboiling points or compounds which form constant boiling mixtures bysubjecting them to radiant energy oi a frequency selected such that onewill absorb energy andtheother will not.

Another object of this invention resides in. the .provision of afractionation method for the separation of compounds having the sameboiling points which utilizes radiant energy for controllingfractionation.

Still another object of this invention resides in the provision oiapparatus which may be utilized with conventional fractionating unitsfor the fur-l of vapors coming into contact with the outer `surfaceofthe-coil. .Directly beneath the coll I8 ther separation oi compoundsby separating those having the same boiling points or which form amixture having a constant boiling point.

This invention further contemplates a vmethod and apparatus forseparating two compounds having the same freezing point since one oithem will absorb radiant energy at a given frequency and the other willnot.

Still another object of this invention resides in the provision of amethod for the separation of compounds having the same boiling point:which can be carried out in a single step or in a series of successivesteps. y

Other objects and advantages of this invention will become apparent fromthe following descrip-V tion when considered with the drawings in whichFigue 1 shows diagrammatically a vertical section of a fractionatingcolumn utilizing the present invention;

' Figure 2 is a fragmentary vertical section, showing diagrammatically.a fractionating tower showingl themanner inwhich the present inventioncan be practiced in a plurality of stages.

Referring to the drawings in detail the simplest form of the apparatusfor practicing the present invention is illustrated by Figure 1 in whichthe casing I0 may be apart of a fractional distillation column. There isprovided at the top of the casing I0 a conventional reiiux head whichcomprises a condensing chamber II. an inlet passageway thereto I2, avalve I3 for controlling the amount of opening into kthe passageway anda cooling coil I4 disposed in the chamber II. Immediately below thereflux head there is provided a vapor product outlet passageway I5. Thebottom of the chamber dened by the casing I0 carries a packing column I5through which vapors from the fractlonating column must pass beforeentering the zone II where further separation of the. vapors is eiectedby subjecting them to radiant energy. Radiant energy is supplied by acoil I8 that is provided with leads I9 which extend through aninsulating plug 20" to a radiant energy source not shown. The coil I 8and leads I9 are formed of tubing through which there is provided a tray20 that is adapted to catch the condensate. The tray 20 is provided witha draw-ci! outlet which extends through the housing I0 to a pointoutside the housing where the condensate may be collected. This outletis provided with a liquid trap 20' which prevents vapors from escaping.

In operation vapor consisting oi two components passes upwardly' fromthe fractionating column through the packing column I6 into the zone I1in which there 'is disposed a multiturn solenoid I8 made of coppertubing. Water or other temperature control medium is passed through thiscoil, and the two components having similar boiling points are passedover the coil f in the form of a vapor at a temperature at which theliquid and gas phases are in equilibrium. For example, for water at '160mm. pressure, this is 100 C., the one component reaching the coil whichis slightly cooler than the vapor, condenses. The other componentreceives suillcient energy from the radiation ileld to keep it in vaporform and to superheat the vapor slightly. This component passes out ofthe housing in the form of vapor.

To insure complete separation of the components-any part or all of thecomponent remain-A ing in vapor form may be admitted to he reilux headand after condensation returned for recycling by the :conduit 2I.

Y In Figure 2 there is illustrated a modied form of apparatus whichillustrates the use of successive stages for effecting a 'greaterseparation of compounds having nearly the same boiling points or aconstant boiling mixture. In this form of the apparatus there is locatedabove the packing column I5, in the bottom of the casing I0, a coolingcoil 22. The cooling coil, as shown, may be provided withdirectingplates 23 which direct all of the vapors coming through the packingcommn It over the comme con 22. Located directly above the cooling coil22 are two sets of electrodes 24 and 25. These electrodes are carried byconductors 26 and 21, respectively, which extend through bushings 28 and29 in the housing III to a radiant energy source, not shown, locatedoutside of the housing I0. Y A bubble -plate 30 is disposeddirectlyabove the electrodes 24 and 25 and in the path of the vapors intheir upward movement. The bubble plate 30 is provided with a liquidproduct outlet 30a. Outlet 30a has a liquid trap 30h which prevents thevapors from escaping. f

Above the bubble plate 30 there are provided bailles 3I which tend toretard the ilow of vapors from the zone above the bubble plate 30 to anext cooling zone in which there is disposed a cooling coil 32 anddirecting plates 33. The cooling coil 32 is, a part o f a second stageidentical to that just described. i

As an example of the operation of this form of the invention water andethyl alcohol form a constant boiling mixture so that it is not possibleto concentrate alcohol by ordinary fractional distillation methodsbeyond purity. It is well known. however, that water being a polarmolecule has strong absorption in the radio frequency spectrum in thehigh frequency region between 1 and 5 centimeters wave length. Alcoholdoes not show equal absorption at points within this region. In fact,important diilerences in power absorption of these materials is alreadyin evidence at 6 megacycles frequency. In order to carry out furtherseparation of these two compounds the mixture is vaporized in anordinary fractionating column and the vapor passed through bubble platesto effect preliminary fractionation. At the top of the column theconventional reflux device isv provided as in ordinary operation, thecolumn being operated at 100% reflux. When the super fractionatingdevice is in operation an auxiliary vapor outlet is provided in theiractionating column slightly below the reflux head, The vapor passesthrough a cooling zone where its temperature is dropped rapidly for afew degrees so that thevaporsare supercooled. Because of the highvelocity of the vapors condensation has not yet taken place. In a narrowzone immediately above the supercooler 22, the vapors are subjected toan intense radio or electromagnetic eld of suflicient wave length thatstrong absorption is caused in the vapor of one component only, forexample, the water. The means for providing this eld is shown in thedrawings as electrodes 24 and 25. As a result of the absorption ofenergy from the radiation field the free path of the water molecules isgreatly increased such that the effective vapor pressure is greater thanthe supercooled alcohol molecules. The vapors next impinge against adetraining device or partial condenser which may be, as illustrated, abubble plate. Fine mesh screens or electrically charged plates such as aCottrel preclpitator can also be used. In this zone the liquied alcoholmolecules are withdrawn through the outlet a and trap 30h While thewater molecules because of their great energy content pass out as vaporthrough theopenings in the baille plate 3|. The vapors rising throughthe openings 3| come into contact with the cooling coil 32 of the secondstage where they are again supercooled and subjected to an intense radioor electro-magnetic field which is supplied by the electrodes 34 of thesecond stage. These vapors next impinge against a second detrainingdevice where any alcohol remaining in the vapors, after they have passedthrough the first stage, is removed and drawn off through the outlet 35and trap 35a in liquid form.

It will be appreciated that a similar separation may be effected betweenhydrocarbons of identical boiling points if they differ in energyabsorption in radiation fields and that multiple stages of more than twomay be employed to eiect still further concentration.

While the invention comprises three steps; supercooling, radiation andcondensation of vapor, the use of the radiation step alone will eil'ectimprovement in separation over that ordinarily obtained byfractionation.

This invention is not limited to radio frequencies but may also beapplied to infra-red visible and ultra-violet radiation. ForV example,the two hydrocarbons given in an example above 2,2,3-trimethyl butane(triptane) and 2,2-dimethyl pentane have similar boiling points. Sincetriptane shows a strong infra-red radiation absorption in the region of120,000 angstrom units at which point 2,2-dimethyl pentane does notabsorb, infra-red radiation absorption of this frequency may be employedto effect separation. In this case the triptane passes out as a vaporwhile the other component returns in the liquid state.

It will be appreciated that with slight modification, this method may beapplied to any other separations involving a change of phase, forexample, the freezing of one component while the tively rich in one ofsaid components, which comprises adjusting the temperature of said uidsystem to a point of incipient phase change, causing phase change insaid system while subjecting the system to radiation Vof saidpredetermined nature, whereby phase changeof one component is inducedwhile phase change ofv another component is suppressed, and separatingphases relatively rich in different components.

2. A method of eiectlng a further separation of petroleum fractionswhich consists of amixture of compounds that have substantiallyidentical boiling points. that comprises the steps of subjecting thefraction while in vapor state to radiations from a. selected portion ofthe radio frequency spectrum, said portion being so selected that atleast one of the compounds in the fraction will absorb radiant energyand at least one other will not, simultaneously subjecting the fractionto a cooling medium whereby the compound that absorbs radiant energywill remain in a vapor state while the compound that does not absorbradiant energy at the selected frequencies will be condensed, therebyseparating the compounds of the fraction.

3. A method of separating the components of a, mixture, at least two ofsaid components having substantially identical boiling points, thatcomprises the steps of separating the mixture into fractions byfractional distillation, separating the components contained inafraction which have substantially identical boiling points byvaporizing the fraction, subjecting the vaporized fraction to radiantenergy of such frequency that one component will absorb energy and theother -will not, simultaneously subjecting the fraction to a. coolingmedium, whereby the component absorbing radiant energy will retain itsphysical state and the one which does not absorb radiant energy at thatfrequency will change state, and separating the two components inaccordance with their physical states.

4. A method of separating a mixture of two compounds, existing in vaporstate, that have substantially identical condensing points, thatcomprises bringing the mixture almost to the condensing point,subjecting the mixture to radiant energy of selected frequency at whichone compound is capable of absorbing energy and the other is not,simultaneously subjecting the mixture to a cooling medium whereby thecompound which absorbs radiant energy at that frequency will remain invapor state and the other will be condensed, and separating thecondensed component from those in vapor state.

5. A method of selectively changing the state of the components of amixture of components which customarily undergo a change in phase atsubstantially the same temperature but having different capacities toabsorb radiant energy of a predetermined nature that comprisessubjecting the mixture to radiant energy of a frequency so selected thatat least one of the components will absorb energy and thereby remain inits original state and at least one other will not, simultaneouslysubjecting the mixture to a. heat exchanger to eiect a cooling of acomponent which did not absorb energy at the selected frequency tothereby change its state, whereby the physical state of at least onecomponent will become ditferent from at least one other component, andseparating the components existing in changed state from the mixture.

CARLETON H. SCHLESMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Baum June 6, 1922 Number Number l0 f.' v

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